抽拉速度对SCN-DC共晶生长形貌的影响

Influence of pulling velocity on microstructure and morphologies of SCN-DC eutectic alloy

本文采用类金属透明模型合金丁二腈-23.6 wt%樟脑(SCN-23.6 wt%DC)合金,研究了棒状共晶定向凝固组织的演化行为,考察了抽拉速度对棒状共晶合金组织形貌演化的影响规律.结果表明,在共晶生长初期,共晶组织首先起源于晶粒晶界或者试样盒型壁处,随后沿液/固界面和平行于热流方向生长;在较小的抽拉速度(0.064—0.44μm/s)下,棒状共晶界面前沿呈现平界面形态,内部两相棒状组织平行生长,并且随着抽拉速度的增大,棒状共晶逐渐细化,棒状间距减小;而在较大的抽拉速度(0.67—1.56μm/s)下,共晶界面前沿呈现胞状生长形貌,胞内的棒状共晶呈放射状生长,同样,随着抽拉速度的增大,胞内棒状共晶逐渐细化,棒状间距减小.

Eutectic solidification is very important in the development of new materials in which the periodic multiphase structures may have a remarkable or enhanced functionality. The morphology evolution during eutectic solidification is investigated experimentally using slab-geometry slides of succinonitrile-（D）camphor （SCN-DC） transparent organic eutectic material. By specifically focusing on the effect of pulling velocity on microstructure in directional growth, the temperature gradient and the thickness are kept the same in all the experiments. It is found that eutectic seeds first occur in the grain boundary channel or the specimen side-wall groove. And the growth of eutectic seeds is both parallel to the direction of temperature gradient and along the liquid/solid interface at the same time. At a low pulling velocity （0.064-0.44 I.trn/s）, the macroscopic growth morphology is flat, and the inner microstructure is rod-shaped, which is parallel to the growth direction. It is obvious that the eutectic spacing becomes smaller with the increase of pulling velocity. At a high pulling velocity （0.67-1.56 p.m/s）, the macroscopic growth morphology becomes cellular. However, the inner microstructure is still rod-shaped, but its distribution is radially outward. And the eutectic spacing decreases as pulling velocity increases.